The present invention relates to an imprinting method and an apparatus therefor. Imprinting is a method in which a molding surface of a mold having very fine projections and recesses formed therein is pressed against a resin applied on a substrate to thereby transfer the shape of the molding surface to the resin.
In recent years, the capacities of hard disk drives have tended to increase and the recording densities of magnetic recording media have thus been increased. As track density increases in accordance with the increase in recording density, a leakage magnetic field is produced from a side surface of a head gap at the time of data writing. The leakage magnetic field causes production of noise to reduce S/N of a playback signal because unnecessary recording called ‘side fringe’ is performed on a region between adjacent tracks.
To avoid such a disadvantage, for example, a discrete track type magnetic recording medium having grooves provided between adjacent recording tracks has been proposed in JP-A-2005-56535. In the discrete track type magnetic recording medium, adjacent tracks are separated from each other so that the ‘side fringe’ problem can be avoided. On the other hand, a patterned medium has been proposed to form 1-bit dots on a disk for the purpose of improving recording density greater.
In either of the discrete track medium and the patterned medium, a minute pattern is formed on a disk. In most cases, the patterning is performed by an imprinting method. The imprinting method uses a mold having a minute pattern formed in a molding surface as a prototype mold for transferring the minute pattern to a surface of a substrate coated with a resin. Thermal imprinting using a thermoplastic resin and photo imprinting using a photo-setting resin are known as the imprinting method. Particularly, imprinting for forming a minute pattern with a nano-meter size is called nano-imprinting.
In the thermal imprinting, a resist pattern is generally formed by the following process. First, after a substrate is placed on a stage, a thermoplastic resin or a photo-setting resin is applied on a surface of the substrate. Then, the substrate and a mold having a molding pattern formed therein are heated to a temperature not lower than a glass transition temperature (Tg) and the mold is pressed against the resist-coated surface of the substrate by a predetermined load. In this condition, the substrate and the mold are held for a predetermined time so that the pattern of the mold is transferred to the resist of the substrate. Then, the mold and the substrate are cooled to a temperature lower than Tg of the resist and the mold is released from the substrate. The substrate having the thermoplastic or photo-setting resin onto which a convex shape corresponding to the concave shape formed in the molding surface of the mold has been transferred is taken out from the stage.
An example of an imprinting apparatus made from three units, that is, a substrate setting unit, a resin coating unit and a processing unit has been disclosed in JP-A-2006-326927. The processing unit performs alignment of a transfer body with a stamper, pressurization and release. In this example, a conveyance robot is disposed in the center while the three units are disposed on the circumference of a circle with the conveyance robot as the center of the circle.
Recently, there has been a method called room-temperature nano-imprinting using SOG (spin-on-glass) or the like (e.g. see JP-A-2005-108351). In this method, the mold is pressed before the resist is hardened by volatilization of a solvent at room temperature, and the mold is removed after the resist is hardened. In this manner, the pattern of the mold can be transferred to the resist. Accordingly, the heating-cooling process can be dispensed with, so that improvement in working efficiency can be attained.
In nano-imprinting commonly known at present, all nano-imprinting steps are performed in one place in one apparatus. The nano-imprinting steps are an alignment step for aligning a pattern of a mold with a predetermined position of a substrate, a heating step for heating the mold and the substrate, a press step for pressing the patterned surface of the mold against a surface of a resist applied on the substrate, a cooling step for cooling the mold and the substrate and a release step for releasing the mold from the substrate.
That is, because a mold provided as an expensive prototype mold produced by electron beam exposure has been heretofore used, it may be said that substrates are one by one subjected to the series of nano-imprinting steps using one mold.
A tact time of 300 or more sheets per hour is however required of either of the discrete track medium and the patterned medium. The required tact time cannot be achieved if all the series of nano-imprinting steps are performed in one apparatus.
The imprinting apparatus disclosed in JP-A-2006-326927 is an apparatus in which: a substrate is set by the substrate setting unit; the substrate is conveyed to the resin coating unit and coated with a photosensitive resin; the substrate is conveyed to the processing unit and subjected to alignment of a transfer body with a stamper, pressurization and release; and the processed substrate is conveyed to the substrate setting unit again and taken out. In the imprinting apparatus, while a substrate is present in any one of the units, any other substrate cannot be loaded because the units are disposed on the circumference of a circle with the conveyance robot as the center of the circle so that the conveyance robot conveys the substrate between the units. For this reason, the configuration of the imprinting apparatus disclosed in JP-A-2006-326927 is the same as in the case where all the series of nano-imprinting steps are performed in one apparatus.
In recent years, it has been possible to produce a large number of clone molds inexpensively from a very expensive prototype mold (e.g. see JP-A-2005-286222). The use of the large number of clone molds has permitted each step to be performed on an assembly line while the mold and the substrate are paired with each other.
In view of the above, it would be desirable to provide a method for performing nano-imprinting efficiently, and an apparatus therefor. The invention was developed in consideration of such circumstances.